This test build is available to Windows Insiders who are subscribed to the Slow ring. These typically entail more polished builds than the ones that first show up in the Fast ring, and features they contain are more likely to end up in the final release that gets doled out to the public.
Adding access to a digital assistant from the Lock screen is not a game changer in a broad sense, but it sure can be more convenient than having to first log into Windows. This is also mostly a play towards freeing up Alexa—no other major AI assistants (Siri, Google Assistant, and to an extent, Bixby) are directly available in Windows 10.
Beyond the tighter integration with third-party assistants (Alexa), the latest test build contains only a few other minor things, such as a fix to allow OEMs to reduce the inking latency based on the hardware capabilities of their devices.
One thing to note is that the added features are turned off by default in the latest test build.
"As mentioned previously, we may ship features in these updates turned off by default and turn them on via controlled feature rollouts. Doing this helps us gain better feedback on overall build quality. With today’s 19H2 build, we are testing this experience. Our plan is to quickly follow-up with another 19H2 build that turns these features on for a subset of Insiders and proceed from there based on feedback and quality," Microsoft says.